1467.pdf

S_pe ctr o mete r.

(

Unde r the d ir e ctio n of L O R I A .TODD

, Ph.D.

)

A po rtab le o_pe n

-path F TIR instr ume nt ha s be e n de v elo_ped, that in c o rpo r ate s a

M

i da c FT I R s_pe ctr omete r, a mod i fi ed

W

h ite c el l, a nd a batte ry pa ck. The de sign in clude s

a r emo v ab le c o v e r fo r the

W

hite c el l_, w h ich al lows fo r e a s e in _path len_{g t}h dete rm in atio n ,

c al i br ation , a nd ba ck gr o und

c ol le ctio n, w h ich a r e chal len ging u sing c o n v e ntio n al ope n

-path FT I R s_pe ctr omete r s. In the n ew in str ume nt, a fol ded ope n

-_path _of _u

p to 12 0 mete r s

is c r e ated u sin_g m ir r o r s an dtwo r etr o r ef le cto r s. Du e to the lo ng path le n g ths w h ich c an

be a ch ie v ed, chemic als c a n be dete cted at the pa rt pe r b i l l io n le v el. In ad d itio n

, the IR

be am is c o ntained w ith in a 6 0 L c el l. T he r efo r e, w he n c o n c entr ations of a chem ic al a r e

dete cted in a r o om_, the lo c atio n of the c o n c e ntr atio n c a n be _pin_pointed.

T he instr ume nt ha s be e n e v aluated in a n e x _po s u r e cham be r u sin _g a r an_ge of

kn own c o n c entr atio n s. T he chemic als u s ed we r e nitr o u s o xi de_, trich lo r o ethyle n e_, a nd

meth_yl et_{h y l k}eton e. T he l imit of dete ctio n wa s c alcu lated fo r e a ch chemic al, and fo u nd

to be in the low pa rt _pe r b i l l io n le v el fo r n i_tr o u s oxi de andtrich lo r o eth_yle n e. Fo r methyl

eth_yl keto n e, the l i m it of dete ctio n wa s fo im d to be appr o ximately 0.1

part s _pe r m i l l io n .

Fo r nitr ous o x i de_{, p}e rfo rma nc e _pa r amete rs_, includ in _{g p}r e c isio n _, a c c u r a c_y, and b ias we r e

e v alu ated ac c o rd in_g t o N I O SH _gu i del in es, andthe instrume nt _performed wel l w ith in the

N I O SH r e c om me n datio n s_, ha vin _{g b i}a s bet te r tha n + /- 10%

a nd a c c u r ac_{y b}et te r tha n

+/- 25%

T he a utho r w ishe s to tha nk the 3M Co r_po r atio n a n dM I D AC Co r_po r atio n fo r their

ge n e r o u s s u_{p p}o rt of th is r e s e a r ch. Gr a nt P lumme r fo r h is te chnic al knowled ge, the

L ist of Tab le s i i

List of F i gur e s iv

L ist of A b breviation s vi

L ist of S ym bols vi i

Intr odu ctio n 1

Ba ck_gr o u nd Information 9

Methods 2 2

Re s ults 2 9

D is c u ssio n 3 5

Co n clu sio n 4 1

Refe r e n c e s . .

A_{p p}e nd ix A

A_{p p}e nd ix B

A_{p p}e n d ix C

A ppend ix D

A_{p p}e nd ix E

A ppe nd ix F

A _{p p}e nd ix G

.4 3

V olume dete rmin ation 4 6

Refe r e n c e S_pe ctr a 5 0

SA S A l_go rithm s 5 6

R o ot

M

e a n Squ a r e Nois e 63

Limits of Dete ctio n a nd

_Q

u a nti fi c a_tio n _{6 8}

Sam_ple Calc ulatio n s 72

Tab le 1 C ha r a cte ristic abs o r_ptio n s 9

Tab le 2

W

a_te r and Ca rbo n d io xi de r e_gio n s 10

T ab le 3 Fla sk Volume s 2 3

T ab le 4 V olume of Tub in _g 2 3

Tab le 5 Co n c e ntr atio n r an_ge s stud ied 25

Tab le 6 Refe r e n c e Spe ctr a Co n c e ntr atio n s a nd Re_gio n s fo r

Q

u a nti fic atio n 2 5

Tab le 7 Path le n_gths us ed 2 6

Tab le 8 A v e r a_ge R

M

S n ois e 29

Tab le 9 Summa r _y of Re s ults 3 0

Tab le 10 Summa r_y of Pr e cisio n, B ia s a n d Ac c u r a cy Re s ults fo r N itr o u s o x i de....3 1

Tab le A - 1 V _olum_e

M

e a s u r eme nts 4 8

Tab le D

-1 R

M

S Nois e 6 5

Tab le E- 1 L imit_{s o}f D_et_{e c}ti_{o n} 70

Tab le E-2 L imi

ts of

Q

ua nti fi c atio n 7 1

Tab le E-3 P_{a r a}m_et

e r s u s ed in L OD a nd LO

_Q

Calc ulatio n s 7 2

Tab le G- 1 0 92 497_a ME K 77

Tab le G-2 0 9 2 89 7

a l

M

E K 8 0

Tab le G-3 0 9 2 9 9 7_a

M

E K 8 4

Tab le G-4 10 0 5 9

7a T C E 8 8

Tab le G-5 1 00 5 97b T C E

a nd

M

E K 92

Tab le G-7 100897_a T C E

. .9 9

T able G- _{8 1 0 1 0}9_7a N i_{tr o u s o x} i d_{e a n} d _TC_{E 1 0 1}

Tab le G-9 ₁0 12 9 7_a N i_{tr o u s o x} i d_{e an} d TC E 10 3

T ab le G-10 10 139 7a N it_{r o u s o x} i d_e 10 6

T able G - _{1 1 1 0 1 397b N i}

tr o u s o x i de 1 08

Tab le G- 12 10 2 2 9 7_a N it_{r o u s o x}i d_{e a}n d SF

e I l l

Table G

-13 120297b ME K a nd T C E 1 14

Table G- 14 0 1 2 898_a Ni_{tr o u s o x} i d_{e an}d T C E 1 1 7

Tab le G- _{15 013 0 9 8}

a N itr o u s o xi de 1 1 9

Tab le G- 16 01319 8_a N it_{r o u s o x}i d_e 12 3

Table G - 1 7 0 2 0 19 8

L is t of F igu r e s

F i gu r e 1

W

h ite c el l O p_tic Co nfi_gu r atio n 5

Fi_gu r e 2 Retr o r efl e cto r 5

Fi_gu r e 3 D is_pe r siv e I R be am _pr odu ctio n 12

Fi_gu r e 4 Dis_pe r siv e I R in str ume nt de si_gn 13

Fi_gu r e 5 Inte rfe r omete r 14

Fi_gu r e 6 Inte rfe r o_gr am 15

Fi_gu r e 7 S in_gle Be am _Spe ctr u m 16

F i gu r e ₈ Cal i br atio n Cu r v e 2 0

Fi_gu r e 9 Fla sk 2 3

Fi_gu r e 10 C ham be r s et

-u_p 24

F i gu r e 1 1 N itrou s o xi de _gr a_ph 3 2

F i_gu r e 12 T rich lo r o eth_yle n e _gr a_ph 3 3

Fi_gu r e 13 Meth_yl eth_y l keto ne gr a_ph 3 4

F i gu r e B

-1 E th_yle n e Refe r e n c e S pe ctr um 5 1

F i gu r e B-2 SF

e Refe r e n c e S_pe c tr um 5 2

F i_gu r e B-3 N i_{tr o u s} O_xi d_e R_ef_{e r e n c e} S

pe ctr um 5 3

Fi_gu r e B-4 T_ri

ch lo r o eth_yle n e Refe r e n c e S_pe ctr um 54

Fi_gu r e B -5

M

_eth

yl Ethy l Keto n e Refe r e n c e S_pe ctr um 5 5

F_{i g}u r e D

-1 R

M

S Nois e 6 8

F i gu r e G- 1 0 9 2 4 9 7_a

M

EK 7 6

F i_gu r e G-2 0 9 2 8 97_al

M

E K 7 9

Fi_gu r e G-5 1 0 0 5 9 7b TCE _{a n}d

M

EK 9 1

F i_gu r e G-6 10 0 6 9 7 b T C E _{a n}d

M

EK 9 4

Fi_gu r e G-7 10 0 897_a TCE 9 8

Fi_gu r e G-8 1 0 1 0 9 7_a N i_{tr o u s o x} id_{e a n}d T C E 1 0 0

Fi gu r e G-9 1 0 12 9 7_a N it_{r o u s o x} i d_{e a}nd T C E 102

Fi_gu r e G- 10 10139 7_a N i_{tr o u s o x}i d_e 10 5

Fi_gu r e G- 1 1 1013 97b N i_{tr o u s o x} i d_e 10 7

F i_gu r e G- 12 10 2 2 9_7a N i_{tr o u s o x}i d_{e a n}d SF

e 1 10

F i gu r e G- 13 12 0297b

M

E K _{a n} d T C E 1 13

Fi_gu r e G- 14 0 1 2898_a N it_{r o u s o x}i d_{e a n}d T CE 1 16

F i_gu r e G- 1 5 0 13 0 9 8_a N i_{tr o u s o x}i d_{e 1}18

F i_gu r e G- ₁6 0₁3 19 8_a N i_{tr o u s o x}i d_{e 1}2₂

L ist of A bbr e v iat io n s

A D C An alo_g to Di_gital Conv ert e r

C O Ca rbo n

M

o n o x i de

F T I R Fo u rie r Tr a n sfo rm Infr a r ed

I R Infr a r ed

LOP I R L o c al iz ed O_pe n

-path Infr a r ed

M

I R A N M iniatu r e Infr a r ed An al_yz e r

N IO SH Natio n al In stit u te of Oc c u_patio n al Safet_y a n_{d H}e alth

S Fe Sul fu r He x afl u o ri de

SN R Si_gn al to Nois e Ratio

R

M

S Ro ot Me a n S_qu a r e

L ist of Sym bols

A Abs o rba n c e

A i A bs o rba n c e of r efe r e n c e s_pe ctr um

A 2 A bs o rba n c e fo r s ample spe ctr um

b Path le n_gth

bi Path le ng th fo r r efe r enc e s_pe ctr um

b2 Pathle ngth fo r s ample spe c tr um

c Co n c e ntr a_tio n

C i Co n c e ntr atio n of r efe r e n c e s_pe ctr um

C 2 Co n c en tr atio n of s am_ple s_pe ctr um

Ci Co n c e ntr ation in

j

ected

Cc Co n c e ntr atio n me a s u r ed in the cham be r

I Inte n sit_y

lo Inte n sit y of ba ck_gr o u nd s_pe ctr um

T Tr ansm it ta n c e

V i Volume in

j

e cted

Vc V olume of the cham be r

In the indu stri al h_{y g i}e n e f iel d, two ge n e r al ty pe s of s ampl in g methods, integr ated

a nd r e al-ti m _e

, a r e u s ed to e v alu ate ga s a nd v apo r c o n c e ntr atio n s. Integr ated s ampl ing

pr o vi de s the ti me wei_ghted a v e r a_ge c o n c e ntr atio n fo r a few kn own chem ic als at a time,

w he r e a s r e al-_ti m _e i_{n str u}m_{e nts c a n}

pr o v i de mo r e detai led e x _po s u r e info rmatio n o v e r ti m e.

In inte_gr ated s am p l in_g, the indu stri al hy gie nist cho o s e s the s ampl ing m ed ia ba s ed o n the

chem ic als of inte r e st in the air, a nd the o nly chem ic als that c a n be qua nti f ieda r e the

chem ic als w h ich ads o rb o nto the med ia. A d d itio n al ly, s ome integr ated methods u s e

chem ic al r e a ctivit_y a s a wa_{y t}o c a_{p t}ur e the c o ntam in a nts. Fo r mo st integr ated methods

,

the s am_pl in_{g m}ed ia mu st be a n al_yz ed in a labo r ato r_y, w h ich c a n take a few days up to a

few we eks.

^ '

In c o ntr a st to inte_gr ated s am p l in _gte chn _{i q}u e s in w h ich the sam_ple s n e ed to be

an al_yz ed in a labo r ato r_y, real

-_ti m_e m_eth_od_s

g ive a n almo st i m med iate me a s u r eme nt of

the c o n c e ntr atio n of a n atmo s_phe ric c o ntam in a nt. Com mo n r e al

-_{ti m}

e methods fo r the

qu a nti f ic atio n of c o ntam in a nts, s u ch a s the miniatur e infr a r ed a n alyzer

(

MIR A N

)

(

ma n ufa ctu r ed b_y T he Fo x bo r o Com_pa n_y in Fo xbo r o,

M

a s s a c hu s et ts

)

qu a nti fy kn own

c o ntam in a nts in r e al-tim_e

; howe v e r, mo st r e al

-tim_e i_{n s}t_{r u}m_{e n}t_{s c a}n

qu anti f y o n l_y o n e

chem ic al at a ti m e an d c a nn ot e a si l_y be u s ed to i de nti f y u nkn own s. M I R A N s a r e ba s ed

a h i_ghe r si_gn al to n ois e r atio

(

SN R

)

a nd h i ghe r r e s olutio n a n d c a n me a s u r e down to _{pp b}

le v els fo r s ome chem ic als

/

^ '_^

In indo o r air _qu al it_y stud ie s a nd c ommu nit_y e x _po s u r e

stud ie s, w he r e e xpo s u r e to multi p le chem ic als at v e ry low le v els is a c o n c e r n , the r e a r e

few r e al-_tim_e i_{n str u}m_{e nts} w_hi_{ch c a n si}m_{u lta n e o u s}l

y me a s u r e a v a riet_y o f chemic als at

v e r_y low le v els

/

^ ^_^

A ls o, in wo rk ing w ith ha z a rdo us mate rials, the i de nti fi c atio n of

u nkn own s is a ma

j

o r c o n c e r n V e r_y few r e al-ti m_e i

n str ume nts al low fo r the i de nti fi c atio n

of u nkn own c o ntamin a nts. Some r e al

-ti m_e m_eth_od_s

, s u ch a s the H n u photoio niz atio n

method

(

ma n ufa ctv i r ed b_y H n u S_ystems In c. in Newto n _,

M

A

)

c a n be u s ed qu al itativ el y to

me a s u r e mixtu r es of chemic als a nd to i de nti f_y s ome unknown s in the air.

A sin_gle r e al

-ti m e method w h ich c a n _qu a nti f_y multi_ple chem ic als si mu lta n e o u sl y

at _{p p}b le v els a nd i de nti f_y unknown s is d i f fi c ult to fi nd. T he r efo r e, the r e is a gap in the

me a s u r eme nt te chn i_qu e s a v ai lab le to the indu stri al h_{y g}ie nist. F T I R spe ctr ometry has

be e n shown to ha v e _pr omis e in fi l l in_g this _ga_p in e n v ir o nme ntal a n d o c c u_patio n al

me a s u r eme nts.

'^ ^ '' ^'^ ^^

U sin _{g F T I R} s_pe ctr ometr_y w ith v e r_y lo n_{g p}ath le n _gths, multiple

chem_ic als c a n be _qu a nti fi ed simu ltane o u sl_y at v e r_y low le v els (p pb

)

. In add itio n to its

ab i l it_y to _qu a nti f_y mu lti_ple chem ic als si multa n e o u sl_y at v e r_y low le v els, FT IR te chnology

al lows fo r the i de nti fi c atio n of u nkn own s_pe cie s u sin_gthe _pat te r n of abs o r_ptio n s in the

fi n_ge r_print r e_{g i}o n of the IR s_pe ctr a.

Two _ge n e r al t_{y p}e s of F T I R s_pe ctr omete r c o nfi gu r atio n s a r e a v ai lab le, ope n

-pa_th

a nd clo s edc el l e xtr a ctiv e. Using ope n

u s ed_; the r efo r e, the method is n o n

-i_{n v a s}i_{v e}

. T he c o n c e ntr atio n me a s v i r ed is the a v e r age

of that c o ntam in a nt c o n c e ntr atio n alo n_{g t}he e ntir e le n _{g t}h of the be am. Point

c o n c e ntr atio n s at lo c atio n s alo n_g the _path c a nnot be kn own u nle s s a n othe r method is

u s ed, s u ch a s tak ing a n a r e a s ample o r u sing be ams that inte r s e ct e a ch othe r, a s in

c om puted tomo_gr a_{p h y}. '''^

'* ' ^^ H

a vin_{g t}he be am o_pe n to the atmo s_{p h}e r e intr odu c e s

d i f fi c ultie s in tak in_g a cle a n ba ck_gr o u nd a nd in c al i br atin_{g t}he _path le n_gth. An abs olutely

cle a n ba ck_gr o u nd ma_y not be a v ai lab le i f the s_ystem is in stal led in a n e n v ir o nme nt w he r e

chem ic als a r e c o n sta ntl_y bein_{g g}e n e r ated o r i f the chemic al is al wa_ys _pr e sent in the

atmo s_{p h}e r e. Calibr atio n is d if fi c u lt be c aus e the r e is n o way to intr odu c e a known

c onc e ntr atio n of a chemic al into the o_pen _path. T h is d i f fi c u lt y can s ometi me s be

o v e r c ome b_{y p}la cin_g a clo s ed c el l in the _path of the be am . A kn own c o n c e ntr atio n o f a

chemic al n ot n o rmal l_{y p}r e s e nt in _the atmo s_phe r e, s u ch a s s ul fii r he x af lu o ri de

(

S F 6

)

, is

ge n e r ated in the c el l, a nd the in str ume nt r e spo n s e is c ali br ated. ^'

'^ ^^

In a clo s ed c el l e x tr a ctiv e F TIR s_pe ctr omete r, the u s e of a clo s ed c el l al lows cle a n

nitr o_gen ba ck_gr o u n ds to be obtain ed, a nd the path le n gth c a n be c al i br ated u sin g a n

eth_{y l}e n e sta nda rd. A ft e r c al ibr atio n_, an air s ample ispumped into the c el l, w he r e the

infr a r ed be am _pa s s e s thr o u _gh the s am p le. T he cel ls in the s e in str ume nts a r e de si gn ed

u sin_g m ir r o r s to c r e ate a fol ded _path fo r the be am. The ty pic al clo s ed c el l fo und in

cha r a cte ristic s of clo s ed c el l e x tr a ctiv e a nd o_pe n- _path FTIR s_pe ctr omete r s. T he n ew

ins tr ume nt is a Lo c al iz ed O pe n- Path In fr a r ed s_pe ctr omete r

(

L O P I R

)

. It in c o rpo r ate s a

MID A C FT I R s_pe ctr omete r

(

ma n ufa ctu r ed b_y

M

I D A C Co r_po r atio n in Ir vin e

, Cal i fo r nia

)

a nd a 6 0 L mod i fi ed

W

hite c el l. L ike a n e x tr a ctiv e F T I R spe ctr omete r, the n ew in str ume nt

ha s a c el l w h ich u s e s m ir r o r s to c r e ate a fol ded IR be am . In th is in str ume nt

, howe v e r, the

W

h ite c el l ha s be e n modifi ed to in clude both the r emo v able c o v e r a nd two r etr o r efl e cto r s.

The c el l c o v e r s c a n be u s edto obtain a cle an nitr o_ge n ba ck_gr o u n d a nd to c al i br ate the

path le n _gth, the n they c a n be r emo v edto al low fo r ope n

-path me a s u r eme n_ts. In o rde r to

c o u nte r a ct the lo s s of l i_ght inte n sit_y a s the l i g ht tr a v els o v e r lo n_ge r d ista n c e s_.

W

h ite c el ls

a r e de si_gn ed u sin_{g p}a r abol ic mir r o r s to r efo c u s the be am with e a c_{h p}a s s thr o u_{g h} the c e_ll.

The r etr o r efle cto r s in th is c el l, s e r v e to elo ngate the path le n gth.

W

he n the be am is

d ir e ctedtowa rd both r etr o r efle cto r s, the le ngth of the be am c a n be tripled.

The sho rte st _path le n_gth _po s si b le in th is _pa rtic ula r c el l is 4 m a n d the lo n_ge st

po s si b le is 120 m . The

path le n_gth c a n be ad

j

u sted in 4 m in c r eme nts betwe e n the

m ini mum a nd ma x i mum _path le n_gths b_y cha n_{g i}n _g the a n _{g l}e of the fi r st _pa r abol ic mir r o r.

Fo r the 4 m _path le n_{g th}

, the be am e nte r s the c el l a nd is r efl e cted by the fi r st pa r abol ic

m ir r o r. It the n h its the fi el d m ir r o r at the bot tom of the c el l a nd is r efl e cted to the s e c ond

pa r abol ic m ir r o r . T he be am is the n r ed ir e cted_, e x its the cel l

, a nd e nte r s the de te cto r

(

s e e

fi el d m ir r o r

to dete cto r fr om s o u r c e

F i_gu r e 1

W

h ite Cel l o_ptic c o nfi_gu r atio n

T he fi el d mir r o r a nd _pa r abolic mir r o r s a r e u s edto obtain _path le n_gths fr om 4 to 4 0

m in le n_gth. To r e a ch path le n gths abo v e 4 0 m, the two r etr o r ef lecto r s mu st be u s ed.

W

he n the be am r e a che s the si de o f the c el l w he r e it wo u l d n o rmal l_y be d ir e cted int o the

dete cto r, it e n c o u nte r s the fi r st r etr o r efl e cto r a nd is r eturn ed alo n g the s ame pathto the

o_ppo site si de of the c el l. T he r e, it e n c o u nte r s the s e c o nd r etr o r efl e cto r a nd is again s e nt

ba ck o n the s ame _pathto the dete cto r

(

s e e F i_gu r e 2

)

. ^^^

l i_ght be am

\

-r etr o r efl e cto r

F i_gu r e 2 Retr o r efl ecto r

r

r

lo n_ge r tha n the t_{y p}ic al 10 m c el l fo u nd in mo st e xtr a ctiv e F T IR in str ume nts. Lowe r

le v els of c o ntam in a nts c a n be dete cted, a nd the LOP IR c a n be u s ed to me a s u r e v e ry low

c o n c e ntr atio n s of chemic als

(

_{pp b}

)

. The c o n c e ntr atio n at o n e lo c atio n can be pr e cis el y

me a s u r ed be c a u s e the _{LO P I R} in v olv e s a lo c aliz ed o_pe n- _path_; the e ntir e _pathle n _gth is

c o ntain ed w ith in a 6 0 L c el l lo c ated at the hei_ght of a huma n br e ath in_g z o n e. T he

in str ume nt its el f fits w ith in a s_pa c e 2 '

6"

x 2'6"x 6'8".

T he LO PI R u s e s a M IDA C

₍

model M2 50 1-C

, s e rial n um be r 20 0

)

s o u r c e. It c a n

be o_pe ra ted o n bat te r_{y p}owe r o r u sin_g ele ctrici_{t y} fr om a n o utlet. T he be amspl itte r is

made of Pota ssium br omi de

(

K Br

)

w ith a Germa n ium

₍

Ge

)

c oatin_g o n o n e hal f. K Br is

tr ans_pa r e nt to infr a r ed l i_{g h}t, a nd Ge is r efle ctiv e. A Ge o n KBr be amspl it te r is ef fe ctiv e

o v e r the r a n_ge o f wa v e n umbe r s fr om 400 to 400 0/cm. On e dr aw ba ck to the K Br

be ams_pl it te r is the fa ct that i t w i l l abs o rb wate r v a_po r a nd fo_g a s ti me _pa s s e s. The

dete cto r is a li qui d nitr o_ge n c o oled

M

e r c u r_y Cadmium T ellu ri de

(M

C T

)

dete cto r. On the

L O PIR, the pr e

-A_{n a}l_o

g to D i_gital Co n v e rte r

(

A D C

₎

_gain is ad

_j

u sted u sin_g

_j

u_mpe r s to

am p l i f_y the si_gn al befo r e it is d i_gitiz ed a nd s e nt to the c om_pute r fo r _pr o c e s sin_g.

T he L O P IR c a n be o_pe r ated in c o n

j

u n ctio n w ith Auto

Q

u a nt Soft wa r e fo r Ga s

Pha s e S pe ctr al An al_ysis

(

a v ailab le fr om

M

ID AC Co r_po r atio n in Ir vin e, Cal i fo r nia

)

. T he

pr o_gr am r e_quir e s a c om_pute r w ith 1 6

M

B of R A

M

to fu n ctio n _pr o_pe rl y. A uto

Q

u a nt

a utomatic al l_y c alc ulate s the sin_gle be am a n dabs o r ba n c e s_pe ctr a fr om _the in_te rfe r o _gr ams

othe r _pa r amete r s u s ed to dete rmin e the c onc e_{n t}r atio n a r e s_pe cifi ed in a method c r e ated b_y

the us e r. To c r e ate a method to a n alyz e a chem ic al c o n c e ntr atio n u sing Auto

Q

u a nt, a

r efe r e n c e s_pe ctr um of the a n al_yte mu st fi r st be s ele cted, w h ich mu st be of the s ame

r e s o lutio n a s the s am_ple s_pe ctr um. In the method

, the path le ngth of the in str ume nt mu st

be s_pe ci fi ed, alo ng w ith the c o n c e ntr atio n of the r efe r e n c e spe ctr um in p pm

* _m

. A

r e_gion of the r efe r e n c e s_pe c tr um is s ele cted fo r the _pr o_gr am to u s e in _qu a nti fi c atio n of

that chem ic al. Fa cto r s in v o lv ed in the choic e of the spe ctr al r egio n fo r qu a nti fi c atio n a r e

the r e_gio n of the s_pe ctr v im, the c onc e ntr ation of the a n alyte, the shape of the pe ak, the

size of the _pe ak, a nd inte rfe r e nt pe aks. A uto

Q

u a nt al lows the ope r ato r to pr e s et the

numbe r of s c a n s to be c o ad ded fo r e a ch me a sur eme nt and the total numbe r of

me a s u r eme nts to be take n. I f de sir ed

, the inte rfe r ogr ams ca n be s a v ed. T he pr ogr am

al low s mo r e tha n o n e ba ck_gr o u nd to be take n at a n_y n um be r o f s c a n s. Multi ple

chemic als c a n be in cluded in the s ame method a nd c a n be _qu a nti fi ed si multa n e o u sl_y.

T he _pu r_po s e of th is r e s e a r ch is to e v alu ate the L O P I R '

s _pe rfo rma n c e in

qu an ti f_yin _g chem ic als u n de r c o ntr ol led labo r ato r_y c o nd itio n s_, w iththe _go al of ha vin_g the

LO PI R a c c e_pted a s a Natio n al In stitute of Oc c u_patio n al Safet y a nd He alth

(

NIO SH

₎

method fo r indu str ial h y_gie n e me a s u r eme nts. The En v ir o nme ntal Pr ote ctio n Age n cy

(

E P A

₎

ha s be e n in v esti ga tin_{g F T} I R methods fo r e n v ir o nme ntal me a s u r eme nts. Cu r r e ntly_,

the r e a r e thr e e _pr o_po s ed te st methods u sin_g e xtr a ctiv e F T I R s_pe ctr omete r s, Method 3 18,

M

ethod 3 2 0, a nd Method 3 21, and a pe rfo rmanc e spe ci fi c atio n fo r Extr a c tiv e FT I R

s_pe ctr omete r s w h ich a r e all awaitin _g fi n al a_{p p}r o v al. '^

-'_' '^'^^

the An al_ys e s of Ga s e o u s Emis sio n s fr om Statio n a r_y So u r c e s. *'_*

' _I

n ad d itio n , the EPA is

als o in v e sti_gatin_g the u s e o f o_pe n

-path F T I R s_pe ctr omete r s fo r e n v ir o nme ntal

a_{p p}l ic atio n s

/

^_'

The L OP I R is a h_ybri d of e x tr a ctiv e a nd o_pe n

-path s_pe ctr omete r

c o nfi gu r atio n s a nd is de stin ed fo r u s e in the e v alu atio n of o c c u_patio n al e x_po s u r e s.

Indu strial h_{y g}ie n e methods a r e e v alu ated a c c o rd in_g to c rite ria _put fo rth b_y N I O S H. '^' "^

In o rde r fo r a n ew method to be a_{p p}r o v ed a s a N I O SH method, c ompr ehe n siv e chambe r

a n d fi el d e v alu atio n stud ie s mu st be _pe rfo rmed. The pr e cisio n

, b ia s, and a c c u racy of the

method n e ed to be dete rm in ed. * ^

In o rde r to be a c c e_{p t}ab le, b ia s mu st be 10% o r le s s

w ith 9 5% c o nfi de n c e. Pr e cisio n is the r elativ e st anda rd de v iatio n of a s et of

me a s u r eme nts fo r al l ge n e r atio n s of a c onc e ntr atio n o r o v e r a r a n_ge of c o n c e ntr atio n s.

The a c c u r a c_y is defi n ed a s the ma xi mum e r r o r of the me a s u r eme nt giv e n a s a _pe r c e nta_ge

of the c o n c e ntr atio n me a s u r ed that is _giv e n w ith 9 0% c o nfi de n c e b_y tha_t method. In

ad d itio n to the _pr e cisio n , a c c u r a cy , a nd b ia s, the l i m it of dete ctio n

(

LO D

)

a nd l i m it of

qu a nti fi c atio n

(

LO

Q)

mu st be dete rmin ed. Inte rfe r e n c e s sho u l d be i de nti fi ed

, a n dthe

ef fe ct of e n v ir o nme ntal pa r amete r s, s u ch a s tempe r atu r e, pr e s s u r e, a nd hum i d ity must be

e v alu ated. *' °' _I

n the fi eld, si de -b

y- _si d

e c om_pa ris o n s w ith a c c e_pted NIOS H metho ds

M ole c ule s c a n take o n e n e r_gy w he n the_y a r e e x _po s ed to ele ctr oma_gn etic

r ad iatio n . The e x tr a e n e rg y c a n bo o st ele ctr o n s to a h ighe r le v el o r c a u s e the mole c ule to

str etch_, be nd_, o r r ot a te. Abs o rptio n of in fr a r ed

(

IR

)

l ight c a u s e s vi br atio n al e n e rg y

cha n _ge s, i.e. str etch in g o r be nd ing of the mole c ule.

W

ith the e x c eptio n of eleme nts,

in o r_ganic s alts_, and d iatom ic mole c u le s

(

O2, N2, C I2

)

, mo st s ubsta n c e s abs o rb in the IR

r e_gio n Not o nl y mu st c om_po u nds ha v e bo nds to abs o rb in the I R , but als o a n y

mo v eme nt of the atoms in the mole c ule mu st c a u s e a rh_yth m ic cha n _ge in the d i pole

mome nt of the c om_po u nd.

M

ole c ule s w ith str o ng d ipole s w i l l u s u al ly ha v e str o n g I R

abs o r_ptio n. The wa v ele n gths abs o rbed by a c ompo u nd depe nd o n the r elativ e ma s s e s of

the atoms_, their bond fo rc e c on sta nts, a nd the geometry of the at oms in the

mole c ule. ^' '

'' '^

T he r e_gio n of infr a r ed l i ght of _gr e ate st inte r e st to chemists is the m i d-IR

(

4 0 0 0 t_o

4 0 0/cm

)

.

^^ °^ _{Th i}

s r e_gio n c a n be d ivi ded into a fu n ctio n al _gr o u_p r e_gio n

(

400 0

-1300 /cm

)

a nd a fi n_ge r_print r e_{g i}o n

₍

13 0 0-9 0 0 /_cm

)

. ^^ '^ _I

n the fu n ctio n al gr o u_p r e_{g i}o n_, c ommo n

cha r a cte ristic abs o r_ptio n s c a n be i de nti fi ed fo r v a rio u s ft mctio n al _gr o u_ps,

(

s e e Tab le 1

)

.

C-C

, C

-0

, C

-N

C= _C

, C

= ₀ , C

=_N , N

=_N

C=_C , C=N

C

-H, 0 -H

, N

-H

13 00-80 0/_cm

19 0 0-1 50 0/_cm

23 0 0-2 0 0 0 / cm

3 8 0 0-270 0/_cm ^ ^ "_^

Tab le 1 C ha r a cte ristic A bs o r_ptio n s

T he functio n al _gr o u_p abs o r _ptio n s can be u s ed to dete rm in e the cla s s of an unknown

c om po u nd, fo r e x ample, w hethe r it is a keto n e, c a rbo xyl ic a c i d, o r o x i de of nitr oge n . The

u s edto i de nti f_ya n u nkn ow n. En a ntiome r s, mole c ule s wh ich a r e mir r o r image s of one

a n othe r, w i l l giv e v e ry si m i la r I R abs o rptio n pat te r n s /

'

IR s_pe ctr a a r e u s ed _qu alitativ el y fo r i de nti fi c atio n of a n u nkn own o r

qu a ntitativ e_{ly t}o dete rmin e the c o n c e ntr atio n of a kn own c om_po u nd. The te chn iqu e c a n

be u s ed o n mo st c om_po u nds, but it do e s ha v e l i m itatio n s. Be c a u s e it pr o vi de s n o

s e_pa r atio n a ndmake s n o d istin ctio n be twe e n mo le c ule s in a s am_ple, it c a n be u s ed o n

si m p le m ixtu r e s w ith a l i m ite_d n um be r of c om_po n e nts. IR spe ctr ometry is n ot go od fo r

a_qu e o u s s olutio n s be c a u s e wate r _giv e s str o n_g abs o r_ptio n in the I R r e_gio n.

^ ' _C a rbo n

d io x i de abs o rbs in the I R a s wel l. T he fa ct that wate r v apo r an d c a r bo n d io x i de a r e

al wa_ys _pr e s e nt in the atmo s_phe r e make s atmo s_phe ric I R m e a s u r eme nts trick_y. T he s e

c om mo n inte rfe r a nt c om_po u nds _giv e str o n _g abs o r_ptio n bands in the fol low in _g r e_{g i}o n s

(

s e e Tab le 2

₎

.

W

ate r

Car bo n d io xi de

3 9 0 0-3 40 0 /_cm 18 50- 13 50 /_cm

2 3 5 0 /cm 6 6 7 /cm ^

' ^_^

Tab le 2

W

ate r a nd Ca rbo n d io x i de Re_gio n s

In o rde r to a v oi d inte rfe r e n c e, the spe ctr al r egio n cho s e n to qu a nti fy the c om po u nd of

inte r e st sho ul d be o utsi de the s e r e_gio n s.

•

In o rde r fo r the info rmatio n fr om a sin_gle be am s_pe ctr um to be u s eful, the spe ctr al

fe atu r e s _pr e s e nt du e to the s am p le mu st be is olated. Va riatio n s in instr ume nt r e spo n s e

a nda n_y c om_po u nds n o rmal l_{y p}r e s en t in _the s am_pl in_g a r e a mu st be a c c o u nted fo r b_y

r ecorded with n o c om_po u n d of inte r e st _pr e s e nt in the be am. T he s amp le a nd ba ck gr o u n d

sin _gle be am s_pec tr a a r e r atio ed, a ndthe abs o rba n c e o r tr a n smis sio n spe ctr um r e s u lts.

A bs o rba n c e a nd tr a n sm is sio n a r e lo_ga rith m ic al l_y r elated te rms :

A= -l_o

gi o

(

%T

)

E qn . 1

w he r e %T =

(

I/I_o

)

W

he r e : A = abs o rba n c e T= tr a n sm it ta n c e

1= inte n sit_y of the s am p le s_pe ctr um Io

= _{inte n sit}

y of the ba ck_gr o u nd s_pe ctr um. '

A bs o rba n c e o r _pe r c e nt tr a n smis sio n is then _{p l}ot ted v e r s u s wa v e n umbe r, g ivin gthe

abs o rbanc e o r tr a n sm is sio n s_pe ctr um.

Fo r _qu a ntitativ e anal_ysis, abs o rba n c e spe ctr a mu st be u s ed be c a u s e the height o r

ar e a o f the abs o rba n c e _pe ak

(

A

)

is_pr o_po rtio n al to the c o n c e ntr atio n of the a n al_yte. The

r elatio n sh i_p fol lows Be e r '

s Law :

A =_{8bc E}

qn . 2

w he r e : A is the abs o rba n c e

₍

hei_ght o r a r e a

)

8 is the abs o r_ptiv it_y of the c om_po u nd in

(p

_pm *mete r s

)

"_^

b is the _path le n_gth in mete r s

a nd c is the c o n c e ntra tio n in _{p p}m . ^ '_^

A bs o r_ptivit_y is a _ph_ysic al _pr o_pe rt_y of the c om_po u nd a n d is a c o n sta nt fo r the s ame

c om_po u nd at the s ame wa v enum be r. ^^ '_^

Nois e is a r a ndom fl u ctu atio n in si_gn al str e n _gth that c a n be c a u s ed b_y man_y

Be c a u s e ele ctric al me a s u r eme nts a r e _qu a ntiz ed, the n um be r of p hoto n s emit ted w il l

fl u ctu ate r a ndom l_y o v e r ti me w ith the n um be r of fl u ctu atio n s _pr o_po rtion al to the s_qu a r e

r o ot of the inte n sit_y of the be am. Sti l l mo r e n ois e c a n c ome fr om the dri ft of ele ctr o nic

c om_po n e nts that c o_me s abo u t du e to cha n _ge s in ma

j

o r e n vir o nme ntal c o nd itio n s, l i ke

tem_pe r atu r e. Th is ty pe of n ois e in c r e a s e s a s the sign al go e s up . Othe r s o u r c e s of n ois e

in clude the motio n of ele ctr o n s in cir c uits, w h ich is indepe nde nt of the inte n sity of the

si gnal.

^^ '^

T he si_gn al to n ois e ra tio

(

SNR

₎

is a me a s u r e of the amo u nt of n ois e in the

me a s u r eme nt c om_pa r edto the si gn al du e to the s am p le. In o rde r fo r a spe ctr al fe atu r e to

be c o n si de r ed " r e al,

"

the abs o rba n c e at that wa v ele n_gth mu st be _gr e ate r tha n thr e e ti me s

the n ois e in the si_gn al. T he L O D fo r a s ubsta n c e is c alc ulated a s the amo u nt of a n alyte,

w h ich w i l l g iv e a n abs o rba n c e _pe ak with a si gn al w ith a n am_{p l i}tude that is thr e e ti me s the

n ois e, o r in othe r wo rds, ha s a n SNR of thr e e. The LO

Q

is c onsi de r edto be the amo u nt

of s ubsta n c e_, w h ich _giv e s a n abs o rba n c e si gn al that is te n ti m e s the n ois e.

^^ ^_^

Ori_gin al l_y, IR spe ctr ometry wa s pe rfo rmed u sin g o n ly d ispe r siv e in str ume nts. In

a d is_pe r siv e s_pe ctr omete r, a prism s epa r ate s the br o ad ba n d be am into its c ompo n e nt

wa v ele n _gths_, a nd a sl it fi lte r s o ut al l bu t the de sir ed wa v ele n_gths

(

s e e F i gv i r e 3

)

.

pn sm

I R l i g ht s o u r c e

(

3

Fi_gu re 3 D is_pe r siv e IR be am _pr odu ctio n

W

he n the _prism r otate s, the wa v elength pa s sing thr o ug h the fi lte r v a rie s. T he

r otatio n of the _prism c a u s e s the in str ume nt to s c a n thr o u_{g h} the infr a r ed wa v ele n_gths, and

the dete cto r me a s u r e s the inte n si_{t y} of the l i_ght. In d ispe r siv e in str ume nts, the be am is

s_{p l i}t into two _pa rts T he fi r st _pa rt tr a v els thr o u_gh the s am_{p l}e c el l, a nd the othe r tr a v els

thr o u_gh a b la nk c el l. The be am that tr a v els thr o u gh the bla nk c el l is the ba ck gr o u nd

(

s e e

Fi_gu r e 4

)

.

to dete cto r

t

sam_{p l}e cel l

I R l i_ght s o u r c e

(

~

^

1

be ams_pl it te r ba ck gr o u n d c el l

to dete cto r^^^

Fi_gu r e 4 Dis_pe r siv e I R in str ume nt de si_gn

F T IR s_pe ctr omete r s u s e the s ame _prin ci_ple s a s d is_pe r siv e IR s_pe ctr omete r s, in that

both t_{y p}e s of in str ume nts u s e IR l i ght abs o r_ptio n to i de nti f_y a nd _qu a nti f_y c om_po u nds.

D is_pe r siv e I R a nd F T IR s_pe ctr omete r s d i f fe r in that FT I R s_pe ctr omete r s take adv a nta_ge

o f c on str u ctiv e a nd de str u ctiv e inte rfe r e n c e of wa v e s to s c a n thr o u_gh a la r_ge n um be r of

wa v ele n_{g t}hs _quick l_y.

Ce ntr al to F T I R s_pe ctr ometr_y is a de v ic e c al led a n inte rfe r omete r, w h ich is

in c o r_po r ated in_to al l FT I R in s_tr ume nts. I t e x p loits the fa ct that l i g ht wa v e s c o n str u ctiv el

a nd de str u ctiv el_{y i}nte r fe r e with e a ch othe r c r e atin _{g p}r ed ictab le inte rfe r e n c e _pat te r n s with

the wa v ele n_gths of I R l i_ght. To a c c om

pl ish th is, a n inte rfe r omete r ha s fo u r br a n che s.

On e br a n ch ho u s e s the I R l i_ght s o u r c e. T he l ight tr a v els fr om the s o u r c e to a

be ams_pl it te r. T he be amspl itte r is tr a n spa r e nt o n o n e half a nd r efl e ctiv e o n the othe r hal f.

As the be ams_pl it te r tu r n s, hal f of the optic al be am is s e nt into e a ch of two br a n che s. In

the f ir st br a n ch is a fi x ed m ir r o r a nd in the othe r is a mo v in_g m ir r o r. T he pa rt of the

be am w h ich h its the mo vin _{g m i}r r o r w i l l ha v e tr a v eled a d is ta n c e w h ich is d i f fe r e nt fr om

the _pa rt of the be am w h ich h it the fi x ed m ir r o r . Ea ch pa rt of the be am bo u n c e s of f a

m ir r o r a n dthe n, at the be amspl it te r, the be am r e c om b in e s a nd is d ir e cted into the fo u rth

br a n ch of the inte rfe r ome_te r. Th is r e c om b in ed be am the n pa s s e s thr o u gh the s am p le a nd

into the dete cto r

(

s e e F i gu r e 5

)

. ^^ '_^

A mo v i n_g mi r r o r

I R _{l i g h}t s o u r c e

(

^

~

\

V

be ams_{p l i}t te r

fi x ed m ir r o r

to s am_{p l}e, dete cto r

^^ '_^

Fi_gu r e 5 Inte rfe r omete r

W

he n the mo vin_{g m i}r r o r a nd the fi x ed m ir r o r a r e at the s ame _{d i}sta n c e fr om the

be ams_{p l i}t te r, al l of the wa v ele ng ths c o n str u ctiv el y inte rfe re in the r e c om b in ed be am, a nd

the si gn al is ma x imiz ed. T h is c o r r e s

po nds to the z e r o _path d i f fe r e n ce

₍

Z PD

₎

. T he

r e s u ltin_{g p}oint in the inte rfe r o_gr am is a h i gh inte n sit_{y p}e ak c al led the c e nte rbu rst. If the

be am w h ich h it the mo vin_g mir r o r w i l l ha v e tr a v eled a dista n c e d if fe r e nt fr om the s e c o nd

pa rt of the o _ptic al be am_, w h ich str u ck the fi x ed m ir r o r. The m ir r o r d ispla c eme nt

(

A

)

is

the d ista n c e of the mo vin_g m ir r o r fr om the _po sitio n of z e r o _path di f fe r e n c e. The

d i f fe r e n c e in the d ista n c e the two be ams tr a v el is c al led the o_ptic al _path d i f fe r e n c e

(

6

)

which is tw ic e the m ir r o r d is_pla c eme nt

(

5= 2 A

₎

. Co n str u ctiv e a nd de str u ctiv e inte rfe r e n c e

in the r e c omb in ed be am c a u s e a _pat te r n c al led the inte rfe r o_gr am w he n the l i_ght r e a che s

the dete cto r.

^^'^ '^

T he inte rfe r o_gr am is the _{p l}ot of l i ght inte n sit_y v s. optic al path

d i f fe r e n c e a n d is the r esult of the su_pe r_po sitio n of the wa v elen _gths _pr e sent in the beam

(

s e e Fi_gu r e 6

)

. ^ '

c

»*«♦

o_ptic al _path d i f fe r e n c e

F i_gu r e 6 Inte rfe r o _gr a_m

A ft e r _pa s sin_g thr o u_gh the s am p le, the optic al be am is r efo c u s ed o nto a dete cto r

fi lame nt. The dete cto r sign al is pr opo rtio n al to the inte n sity of the I R l ight that h its it. I R

p hoto n s a r e abs o rbed, givin g the ele ctr ons in the dete cto r fi lame nt h i g he r e n e rg y. Ha ving

h i_ghe r e n e r_{g y} ele ctr o n s is n ot e n o u _gh to _pr odu c e a si gn al. A v oltage is ap p l ied a c r o s s the

fi lame nt, a nd the h i gh e n e rg y ele ctron s ge n e r ate a n ele ctric al c u r r e nt. Th is c u r r e nt is

T he si_gn al mu st be c o n v e rted fr om a c u r r e nt to a _{d igit}al si_gn al that the c om_pute r

c a n u nde r sta nd. This c o n v e r sio n is acc ompl ished by the a n alog to d igital c o n v e r te r

(

A D C

₎

. The A D C is made u

p of b its. T v«o r ais ed to the powe r of the n um be r of b its is

the la r _ge st si gn al that c a n be ha nd led b_y the ADC. A n AD C w ith a h igh n um be r of b its is

de sir ab le. The d yn amic r a nge of the AD C is the di ffe r enc e betwe e n the h ighe st a nd

lowe st si_gn als it c a n hand le. In F T IR_, the siz e of the c e nte rbu r st is the sign al str e ngth

that dete rm in e s how much of the A D C d_yn amic r a n_ge is u s ed. If the ce nte rbu r st is to o

la r _ge, the inte rfe r o gr am is c ut of f, a nd the SNR w i l l n ot be i mpr o v ed by c o ad d ing spe ctr a.

To ad

j

u st the siz e of the inte rfe r o_gr am c e nte rbu r st, the gain s ett in g is u s ed. ^ ^'

A ft e r the in te rfe r o _gr am is d i g itiz ed a nd r e a che s the c om_pute r, the Fo u rie r

Tr a n sfo rm is the mathe_matic al tr a n sfo rmatio n that cha n_ge s the inte rfe r o_gr am, a plot of

inte n sit_y v s. optic al path d i f fe r e n c e, to a single be am spe ctr um, a plot of inte n sity v s.

wa v e n vmibe r

(

s e e Fi_gu r e 7

₎

. '^^ '^

c

ff'%^* !>

W

a v e n um be r

(

cm

'

)

FT IR s_pe ctr omete r s ha v e ma n_y adv an ta_ge s o v e r dis_pe r siv e I R in str ume nts. T he s e

adv a nta_ge s in clu de a h i_{g h}e r _SN_R a nd _gr e ate r s e n sitiv it_y and _pr e cisio n . The SNR a nd

s e n sitivit_y of a n F T I R s_pe ctr omete r a r e bet te r tha n tho s e of d is_pe r siv e in str uments

be ca us e al l wa v ele n _{g t}hs of the l i_ght r e a ch the dete cto r at the s ame ti me, a s c ompa r ed to a

dis_pe r siv e in str ume nt w he r e o nl_y a few wa v ele n_gths r e a ch a dete cto r at a n_y o n e time.

The s e n sitivit_y of the dete cto r in c r e a s e s w ith the inte n sit_y o f the IR l i_ght that r e a che s the

detecto r. The fa ct that al l of the wav ele ngths r e a ch the dete c to r at the s ame ti me g iv e s a

bet te r SNR be c a u s e a n_y n ois e _pr e s e nt in the si_gn al is sha r ed amo n_g al l of the

wa v ele n _gths.

^' ''^ '^

A d d itio n al r e a s o n s fo r bette r SN R in FT I R in str ume nts _tha n in d is_pe r sive

in str ume nts in clu de the fa ct that FTI R s_pe ctr omete r s allow s c a n s take n at c o n stan t

r e s olutio n to be c o ad ded, s o that r a ndom f lu ctu atio n s in the si gnal w i l l c a n c el e a c h othe r

o u t, r edu cingthe n ois e. Using mo r e c o ad ded s c a n s w i l l giv e a bet te r SNR. In ad d itio n ,

the n ois e in me a s u r eme nts de_pe nds o n the amo u nt of the ti me s_pe nt me a s u rin_g that

wa v e n um be r. F T IR in str ume nts spe nd m u ch m o r e ti m e obs e r vin g e a ch wa v ele ngth

du rin_g e a ch s c an c om pa r ed_to d is_pe r siv e in str uments.

^" '^ '^

FT I R s_pe ctr omete r s als o ha v e _gr e ate r _pr e cisio n than d is_pe r siv e I R in str uments

beca u s e the_y in c o r_po r ate a Hel ium-N

e o n la s e r a s a n in_te rnal wa ven umbe r sta n _da rd.

T he se la s e r s ha v e a wa v e n umbe r of 15,7 9 8.6 3 7 /cm, a nd al l the I R wa v e n um be r s are

me a s u r ed r elativ e to it. T he la s e r is als o u s ed to tr a ck the

po sitio n of the mo vin_g m ir r o r .

la s e r w i l l c on str u ctiv el_y inte rfe r e e v e r_y 0.63 2 |Lim. The dista n c e the moving m irr o r ha s

tr a v eled is dete rm in ed u sin_g the n um be r of ma x ima in the inte rfe r o _gr am of the la s e r. On e

l i m itatio n of the F T I R sin _gle be am te chni_qu e is that the ba ck gr o u nd is me a s u r ed at

a n othe r ti me tha n the sam p le_, c om_pa r ed w ith d is_pe r siv e I R s_pe ctr o s c o_{p y w h}e r e the

ba ck gr o u nd is c ol le cted at the s ame time a s the s am_{p l}e. ^^ ^'^ ^^

Re s olutio n_, SN R_, and s am p l in_{g t}i me af fe ct e a ch othe r, a n d mu st be opti m iz ed

a c c o rd in_g to the n e eds of the s am_ple. R e s olutio n is a me a s u r e of the in str ume nt '

s ab i l it_y

to dete ct s_pe ctr al fe atu r e s that a r e clo s e to e a ch othe r. In o rde r to r e s olv e fe atu r e s , the

wa v ele n_gths at w h ic_{h th}e fe atu r e s a_{p p}e a r mu st _go in , the n o ut, and fi n al ly ba ck into

pha s e. In c r e a sing the optic al path d i f fe r e n c e giv e s bet te r r e s olutio n . A t h ighe r

r e s olutio n s, the r e a r e mo r e data points. T he n um be r of data points c a n be dete rm in ed by

the fo l low in_g e_qu atio n :

W

a v e n umbe r r a n_ge / r e s o lutio n = n umbe r o f data _points. E qn .3

Be c a u s e r e s o lutio n is a me a s u r e of the minimum d ista n c e s e_pa r atin_g two fe atu r e s at

w h ichthe_y c a n be d is tin_guished o n a s_pe ctr um, r e s olutio n improv e s a s the n um be r

de s c ri b in_g it de c r e a s e s. ^^ '_^

C ha r a cte ristic s of the s am_{p l}e c a n c o ntri bute to _po o r r e s olutio n . T he w i dth of the

abs o rba n c e ba nds fo r a n _y c om po u n d de_pe nd o n the n um be r of inte r a ctio n s that s_pe cie s

has w ith d i f fe r e nt chem ic al e n vir o nme nts. The n um be r of chemic al e n vir o nme nts a

man _y d i f fe r e nt t_{y p}e s of mo le c u le s a r e in the s am_ple. In a s ample that c o n sists of o n e

pur e s ubsta n c e, the spe cie s of inte r e st

o nl_y c ome s into c o nta ct w ith its elf_; it ha s few

chemic al e n vir o nme nts. T he w i dth of the ban ds is als o in f lu e n c ed b y the atmo sphe ric

c o n d itio n s of the s am_ple, s u ch a s the tempe r atu r e a n d pr e s s u r e. In o r de r to opti m iz e the

time fo r the me a s u r eme nts, the r e s olutio n sho uld be s et s o that it is 4

-5 _ti m_{e s} b_{et te r t}h_{a n}

the n a r r owe st _pe ak. In ga s e s, the mole c ule s a r e v e ry fa r apa rt and inte r a ct w ith few othe r

mole c ule s_{; t}hu s_, the_y ha v e v e r_y n a r r ow ba n ds.

W

hen me a s u rin gga s e s, h igh r e s olution is

n e ededto r e s olv e the s_pe ctr a. *^ ^'

N ois e in c r e a s e s a s the r e s olutio n i m_pr o v e s be c a u s e the n ois e is c o n sta nt o v e r the

w hole inte rfe r o_gr am. At h ighe r res olu tio n s, the optic al path d i ffe r e n c e is lo nge r, the

inte rfe r o_gr am w ill ha v e lo n _ge r si de a rms, a nd the n ois e wi l l be a h i ghe r pe r c e ntage of the

total si_gn al. To obtain a h igh SN R at h igh r e s olutio n, it is be st to c o ad d ma ny s c an s

The h i_ghe r the num be r of s c a n s, the h ighe r the s am p l ing ti me. Thu s, the ope r ato r mu st

de cide to bala n c e a r e a s o n ab le s am_{p l i}n_g ti me with hi gh r e s olutio n a nd a _go od SN R. ^^ ' '

The n ois e in the me a s u r eme nts is r e_po rted asr o ot me a n s_qu a r e

(

R

M

S

)

n ois e. It is

c alc ulated b_y tak in_g two ba ck -to -b

a ck me a s u r eme nts a n d u sin_g the f ir st a s the

ba ck_gr o u ndto c r e ate a n abs o rba n c e s_pe ctr um w ith the s e c o nd. A r eg io n of the spe ctr um

1 0-2 0 d_ata

points in w i dth is s ele cted in a n a r e a of inte r e st. In the r eg io n cho s en

, a be st

fi t lin e is _plot te_d, a nd the r o ot mea n squ a r e d i f fe r e n c e of the data

points fr om _the l in e is

c alc u lated. R

M

S n ois e is a n i mpo r ta nt pa r amete r fo r tr a ck in

g in str ume nt _pe rfo r_man c e

In F T IR a n al_ysis, qu a nti fi c atio n of chemic al c o n c e ntr atio n s is pe rfo rmed u sin g

r efe r e n c e s_pe ctr a. Be c a u s e B e e r '

s Law is a s s umedto be l in e a r, the c ali br atio n c u r v e is

the l in e fr om the _point

₍

0,0

)

to the po in t g iven by the r efe r e n c e spe ctr um on a c u r v e

plot teda s abs o rba n c e v s. c o n c e ntr atio n . In th is plot, the c o n c e ntr atio n is giv e n a s the

pr odu ct of the c o n c e ntr atio n in _{p p}m a nd the _path le n _gth u s ed fo r data c o l le ctio n in mete r s

(

s e e F i gu r e 8

)

.

X) <

(p p

m* _m

, A

)

Fi_gu r e 8 Cal i br atio n c u r v e

Co n c en tr atio n

(p p

m* _m

)

T he c o n c e ntr atio n s of the r efe r e n c e s_pe ctr a a r e _given a s the _pr odu ct of c o n c e ntr atio n a n d

path le n _gth, p p m * _m

, s o that the abs o rbanc e, A ^^_eb_c i

s sta nda rd iz ed. A n in str ume nt w ith

a n_{y p}ath le n_gth c a n be u s edto c ol le ct the s am_ple s_pe ctr a.

W

ith the path le n

gth an d

abs o rba n c e kn own, the c o n c e ntr atio n c a n be fo u nd:

bl C l^ 2 C 2=A l/ A E_qn. 4. 1

s o, A2bi C ]/ A ]b2 =

C 2 E_qn. 4.2

w he r e_, A i is the abs o rba n c e o f the r efe r e n c e s_pe ctr um

b] C i is the c o n c e ntr atio n o f the r efe r e n c e s_pe ctr um in _{p p}m* m

ba is the _path le n_gth fo r the s am_ple s_pe ctr um

In o rde r to be a c c u r ate, t he r efe r e n c e spe ctr um c o n c e ntr atio n in p pm

* m m

u st be

h i_ghe r than the s am_{p l}e c o n c entr ation in _ppm*m. In ad d ition

, the r efe r e n c e and s amp le

M

et hods

T he L O P I R wa s _pla c ed in side a stainle s s ste el cham be r, 2 '

6" x 2

' 6"

x6 '

8"

, wh ich

wa s 10 19 L in v olume w ith the in str ume nt in si de. T he cham be r hadtwo 4

"

e x ha u st

v alv e s. On e of the s e e xha u st v alv e s c o ul d be ope n ed fo r make

-u_p air

, a nd the othe r wa s

c o n n e cted to the labo r ato r_y e xha u st s_ystem. T he cham be r als o had fo u r 1/4

"

Swa_gelok

port s. T wo of the S wagelok port s we r e u s ed fo r the pump in

j

e ctio n s, a nd two we r e u s ed

fo r s_yrin _ge in

j

e ctio n s.

C hem ic al s ele ctio n wa s ba s ed o n to xicit_y, T LV , u s age in indu stry, fu n ctio n al

gr o u_ps, a nd str u ctu r e. Fr om an initial l ist of chemic als c om mo nly u s ed in in du stry,

chemic als, w h ich we r e simi la r in structu r e a n d fu n ctio n al gr o up, we r e el i m in ated. T he

adv e r s e he alth ef fe cts, w h ich the TLV wa s s et to pr e v e nt, we r e take n into a c c o u nt, a nd

the chem ic al w ith the lowe r to x icit_{y w}a s cho s e n . The chem ic als s ele cted had v a ried

str u ctu r e s a nd fu n ctio n al _gr o u_ps, in clud ing a keto n e gr o up, a n o x i de of nitr o ge n, a nd a

ch lo rin ated h_ydr o c a rbo n.

K n own c o n c e ntr atio n s of trich lo r o eth_yle n e, methyl ethyl keto n e, a ndn itr o u s

o x i de we r e _ge n e r ated in the cham be r _{b y i}n

j

e ctin_{g 5}00 _{p pm g}a s e s in nitr o_ge n

₍

+/ -1%

₎

.

T he in

j

ectio n v olumeswer e _ge n e r ated u sin_g s_pe cial l y made filter fl a sks. F i lt er fl asks

fr om 12 5 to 20 0 0 m L we r e alte r edto in clu de two a rm s 1/4" in d iamete r. On e a ch a rm

was a sto_pc o ck and Swa_gelok c o n necto r . In ad d itio n , the o rigin al a rm wa s remo v ed, a nd

Swa_gelok

sto_pc o ck

sto_pc o ck

Swa_gelok

F_{i g}u r e 9 Fla sk

T he v olume of the fl a sks wa s dete rmin ed b_y fil l in_g the fl a sk w ith wate r a n d

me a s u rin _gthe amo u n t of wate r in e a ch fl a sk w ith _gr adu ated c_yl in de r s. T h is pr o c e s s wa s

r e_pe ated thr e e ti me s fo r e a ch fl a sk

(

s e e Table 3

)

.

F la sk siz e

(

mL

)

125

250

5 0 0 10 0 0

10 0 0

2 0 00

2 0 0 0

A ctual v olume

(

mL

)

17 5 2 8 0 5 87 118 0

117 5 2 1 9 4

2 12 3

Standa rd de viatio n

0.5 8 5.0 3

1.73 0.5 8

1.15

0.96 2.2 2

T ab le 3 F la sk Volume s

The v olume of the tub in_g u s ed in the e x_peri me nts wa s fo u nd u sin _g the d iamete r

a nd len_gth of e ach p ie ce of tub in_g

(

s e e Tab le 4

)

.

Tub in _g Volume

(

m L

)

B l 3 2. 1

B2 3 9.0

B3 3 2.4

Fo r e a ch e x_pe rime nt, thr e e ba ck gr o u n ds we r e take n at 2 5 6 s c a n s. Beg inning in

Ja n u a r_y 19 9 8, a nitr oge n pu r ge wa s pe rfo rmed in the cham be r prio r to tak ing the

ba ck_gr o u n ds a n d _ge n e r atin _g the s am_ple. The in

j

e ctio n wa s pr epa r ed by f low in g 50 0p pm

ga s thr o u _gh a f la sk u nti l the n um be r of air e x cha n_ge s wa s suf f icie nt fo r the e ntir e v olv ime

of the f la sk to be 50 0_{p p}m, at le a st 2 0 m in ute s. The stopc o cks we r e clo s ed, a nd the n the

f la sk wa s c o n n e cted to the cham be r in s e ries w ith a _pum_p.

e xha u st v alv e

pum_p

fl a sk

Fi_gu r e 1 0 C ham be r s et-_u p

A ir wa s _pum ped fr om the cham be r, thr o u gh the fl a sk, a nd ba ck into the cham be r.

The _pum_p wa s al lowed to r u n u nti l the c o n c e ntr atio n me a s u r ed b_y the L O PI R r e a ched

ste ad y state_, a nd the n the _pum p wa s tu r n ed of f_, aft e r w h ich fi v e me a s u r eme nts at 12 8

s c a n s _pe r me a s u r eme nt we r e a v e r a_ged. T he a v e r age c o n c e ntr atio n me a s u r ed wa s

c om_pa r ed w ith the e x _pe cted c o n c e ntr atio n . T he e xpe cted c o n c e ntr ation wa s c alc ulated

V ,

* _C

i= V c* Cc

So , Cc

=_V

i* Ci/V c

E qn. 5.1

E_qn . 5.2

W

he r e, V iwa s the v olume in

j

e cted

Ciwa s the c o n c e ntr atio n in

j

e cted

Vc was the total v o lume of the chambe r, tub ing, and fl a sks

And Cc wa s the c o n c e ntr atio n c alc ulated in the cham be r.

The v olume of the cham be r wa s dete rmin ed w ith the in str ume nt in si de the cham be r

(

s e e

A _{p p}en d ix A

₎

. The r e s olutio n wa s 0.5 /cm, and tria ng le apod iz ation wa s u s ed. Ea c h

c o n c e ntr atio n wa s r e_pe ated a ta r_get of fo u r ti me s

(

s e e Tab le 5

₎

.

C hem ic al

N itr o u s o x i de

Trich lo r o eth_y le n e

Meth_yl eth_yl keto n e

Ra n_ge

0.0 8 5 5 - 0

.86 2 p pm

0.0 84 4 - 1

.0 56 p pm

0.0 8 5 3

- 0

.2 8 6 p pm

Tab le 5 Co n c e ntr atio n r a n_ge s stud ied

T he Ha n st l ibr a r_y r efe r e n c e s_pe ctr a we r e u s ed fo r the _qu a nti ficatio n of nitr o u s

ox i de, trich lo r o ethyle n e, a n d methy l eth y l keto n e. 3

M

ge n e r ated r efe r e n c e spe ctr a we r e

used fo r the _quanti fi c ation of eth_y le ne a nd S Fe

(

s ee Tab le 6

)

.

(

Fo r e x amp le s of r efe r e n c e

s_pe ctr a, s e e Ap pe ndix B.

)

C hemic al _Refe r e n c e Co n c e ntr ation Re_{g i}on fo r

Q

ua nti fi c ation

Meth_yl eth_yl keto n e 762 p pm* m 1 1 4 4.0 - 12 3 3.9 /cm

T rich lo r o eth_yle n e 2 82 _{p p}m* m 9 0 9.7

- 9 67 .4 /cm

N itr o u s o xi de 80 _{p p}m * m 2 17 4.9 - 2 2 55.0 /cm

Sul fu r he x afl uo ri de 2.9 9 p pm

* _{m 9 3 8}

. 1

- 10 17

.4 /cm

Eth_yle n e 2 0 6.6 ppm

*_{m 8 5 8}

.7 - 1 13 2

.0 /cm

Tab le 6 Refe r e n c e s_pe ctra c o n c e ntr atio n s a nd r e_{g i}o n s fo r _qu a nti fi c ation

W

ith the c o v e r s o n the in str ume nt, o n e ba ck gr o u nd wa s take n at 2 5 6 s c a n s, a nd the n ultr a

h i_{gh p}u r it_y n itr o_ge n wa s f lowed thr o u _gh the c el l u nti l the s_pe ctr al wate r l in e s sto_{p p}ed

be c om in_g n e_gativ e. T he nitr oge n f low wa s c o ntin u ed w h i le thr e e ba ckgr o u nds we r e

take n at 2 5 6 s c a n s. T he n ethy le n e wa s al lowed to f low thr o ugh the c ell u nti l the

c o n c e ntr atio n r e a ched a ste ad y state. ^' ^_^

Ea ch me a s u r eme nt wa s _pe rfo rmed b_y c o ad d in_g

12 8 s c a n s. Fiv e me a s u r eme nts we r e a v e r a

ged, a n d the pathle ngth wa s the n c alc ulated:

BiCi = B2C2 E_qn . 6. 1

s o_, B2= B]C,/ C2 Eqn . 6.2

w he r e : B i wa s the o r i_gin al _pathle n _gth

Ci wa s the c o n c e ntr atio n me a s u r ed

B2 wa s the new, c alc ulated path le n gth

a n d C2 wa s the c o n c e ntr atio n of eth_yle n e in the c_yl inde r

₍

s e e T a_{b l}e 7

₎

.

Da_te

8 /20 / 97

1 0/4/ 97

1/ 1 3/ 9 8

Path le n _gth

3 0.6 6

3 6.2 8

3 9.4 3

Tab le 7 Path le n_gths u s ed

The data we r e an al_yz ed fo r b ia s_{, p}r e cisio n, a n d a c c u r a cy, a s wel l a s L O D a nd

LO

_Q

. B ia s, pr e cisio n, a nd a c c u r a cy we r e c alc u lated u sin g the method pr e s e nted in the

N I O SH Gui del in e s fo r Sam_pl in_g a nd Anal_ytical

M

ethod De v elo_pment a n d Ev alu ation

A ppe nd ix 1

, a s s umin g that the b ia s wa s n ot known , a nd the tr u e c o n c e ntr atio n s we r e

known _by stoich iometr _ic dete rm in atio n . Pr e cisio n was defi n ed a s the r elativ e sta nda rd

deviatio n of a s et of mea s u r eme nts a_t c o n c e ntr atio n i. T he equ atio n u s edto fi n dthe

J H i

Sri 2=

/

I 2

(

Ci_ji- Ci_j

)

'

E qn . 7

J

₍

ni - 1

)

C

j

W

he r e : J wa s the n um be r of _ge n e r atio n s of c o n c e ntr atio n i

H i wa s the n um be r of me a s u r eme nts du rin _g e a ch _ge n e r atio n of i Ci_jiwa s a sin_{g l}e me a s u r eme nt

Cj_j wa s the a ver age of the me a s u r eme nts du rin_g e a ch ge n e r atio n of i

Ci wa s the a v e r a_ge of the me a s u r eme nts o v e r al l _ge n e r atio n s at i

/

" '^

T he b ia s wa s defi n ed asthe r elativ e d i f fe r e n c e betwe e n the mea n of the me as ur eme nt s

and the c alc ulatedc o n c e ntr atio n. T he equ atio n u s ed to fi nd the b ia s fo r e a ch

c o n c e ntr atio n _ge n e r ated wa s :

Ci

Bi = - 1

E qn. 8 e i

W

he r e : &i wa s the c alc ulated c onc e ntr ation

C_i wa s the a v e r a_ge of me a s u r eme nts o v e r al l _ge n e r atio n s of c o n c e ntr atio n i^ ^_^

T he o v e r al l b ia s wa s c alc ula_ted u sin_g the fol low in_g e_qu ation:

^ _{S B}

i

B =

E qn. 9 k

W

he r e :k wa s the n um be r of c o n c e ntr atio n s _ge n e r ated And Bjwa s the b ia s at e a ch c o n c e ntr atio n i.

^^°^

T h is e_quatio n a s s umed that the n umbe r of me a s u r eme nts _pe r _ge n e r ation of e a ch

c o n c e ntr atio n we r e e_qual a ndthat the n um be r of ge n e r atio n s _pe r c o n c e ntr atio n we r e

e_qu al. T he po oledpr e cisio n wa s c alc ulated u sin g the fol low ing equ atio n :

S_„

_^

i :

₍

f,

(

S™

)

'

/ f

₎

_{E q}n . 1 0

W

he r e : S_{r xi} is the _pr e cisio n at e a ch c o n c e ntr atio n fi is de_gr e e s of fr e edom, m

- 1

a nd f is the s um of al l fi * ' °_^

W

he n c alc ulatin_g the _po ole_{d p}r e cisio n a nd s ubs e_qu e nt c o nfide n c e statistic s fo r

pr e cisio n , the r e c om me n ded pum p e r r o r of 0.0 5 wa s n ot in cluded be c a u s e the L OP I R d i d

n ot u s e a _pum_p. The 9 5% c o n fide n c e inte r v al fo r po oled pr e cisio n and o v e r al l b ia s

, as

well a s the a c c u r a c_y a nd 9 0% c o nfide n c e inte r v al fo r a c c u r a c_y we r e c alc ulated u sin _ga

SA Sal go rit_{hm p}r e s e nted b_y NIO SH

₍

s e e A_{p p}e nd ix C

)

.

^" ^_'

T he a c cu r a c_y is c alc ulated in

two wa_ys b_y the al go rithm :the Bo nfe r r o ni _pr o c edu r e a nd the h_{y p}e rbol ic a_{p p}r o x i matio n .

Fo r trichlo r o et_{h y}le n e a nd m eth_yl eth_yl keto n e, the N IO SH r e c om me nded method

fo r c alc ulatin _g the _po oled_pr e cisio n a n d o v e r al l b ia s we r e n ot a_{p p}l ic ab le be c a u s e the

Re s u lts

In o rder to fi nd the L O D a nd L O

Q

, ba ck to ba ck sin gle be am spe ctr a we r e u s ed to

make an abs o rbanc e s_pe ctr u_m. The R

M

S n ois e wa s c alc ulated in thr e e r egio n s : 9 7 0

- 9 5 0

,

12 90- 1270

, a nd 2 8 40

-2 8 20

(

_{s e e}

A p pe nd ix D

)

. The a v e r age R

M

S n ois e wa s c alc ulated in

e a ch r e_gio n a nd fo u n dto be 1.8x 10 "^

in the r e_gio n of the s_pe ctr um fr om 97 0- 9 5 0 /_cm

,

3.3x 1 0

"^

in the r e_{g i}o n fr om 129 0- 12 7 0 /_cm

, a nd 3.3x 10

"^

in the r e_gion fr om

2 84 0-2820 /_cm

(

_{s e e} T _ab l_e 8

)

.

Re_gio n 9 7 0-9 5 0 /

cm 12 9 0- 12 7 0 /_cm

^

2 84 0-2 8 2 0 /

cm

A v e r a_ge R

M

Sn ois e l.Sx l O -'

3.3x 10 3.3x 10

"

Tab le 8A v e r a_ge R

M

S n ois e

The L OD a nd L O

Q

we r e c alc ulated usin_g the R

M

S n ois e c alc ulated fo r e a ch

r e_{g i}o n o n e a ch date

(

s e e A p pe nd ix E

₎

. T he lowe st l i m it of dete ctio n at a 4 0 m path le ng th

wa s 0.0 09p pm fo r nitr o u s o x i de

, 0.015pp m fo r trich lo r o ethyle n e, a n d 0. 11 1ppm fo r

meth_yl eth_yl keto n e. T he lowe st l i m it o f qu an ti fi c atio n at a 4 0 m path le n g th wa s 0 .0 32

pp m fo r nitr o u s o xi de, 0.05 p pm fo r trich lo r o eth y len e

, and 0.3 7 1 fo r methyl eth y l keto n e

(

s e e Tab le 9

)

.

Fo r trich lo r o eth_yle n e_, w he n the me a s u r edc o n c e ntr atio n s w e r e _plot ted v s. the

c alculated c o n c e ntr atio n s_, the be st f it l in e had a slo_pe o _{f 0}.94 0 3, inte r c ept of 0.0 16 3_, a nd

R^ v alu e of 0.99 8 4

(

s e e Fi gu r e 1 2 a nd T able 9

)